This project is a request for funds for an expanded Core Flow Laboratory by an existing user group at Tufts University School of Medicine: Drs. Brigitte T. Huber (P.I.), Brent Corhan (Co-P.I.), Claire Moore (Co- P.I.), Naomi Rosenberg (Co-P.I.), David A. Thorley-Lawson (Co-P.I.), and Henry H. Wortis (Co-P.I.). The current facility, consisting of a FACStar Plus and a FACScan, has been in operation for the past 10 years and has been self-supported and upgraded through fees charged to users, most of which are paid from NIH-funded grants. Thus, the technical expertise is in place. An expansion is requested for two reasons: a) the current equipment is in need of substantial improvements to remain current, and b) state of the art techniques in cell cycle analysis and phenotyping require the use of a 4 color instrument and a HeNe laser. The projected use by this core group, all funded through RO1 grants, is 75%, which leaves 25% for other investigators at Tufts University School of Medicine. The facility will be run under the overall direction of the P.I., with direct supervision by the Flow Laboratory manager and a full time operator. The overall benefit of the expanded Core Flow Laboratory for the user group in particular, and the Basic Sciences faculty at Tufts University School of Medicine in general, will be considerable, because it will allow the full faculty at Tufts University School of Medicine in general, will be considerable, because it will allow the full benefit of the NIH sponsored research commitment. The institutional support has been guaranteed.